Process of producing chromic-acid solutions



Patented pr. 29, 1924.

PROCESS OF PRODUCING CHRONIC-ACID SOLUTIONS.

Ho Drawing.

To all whom z'tmay concern:

Be it known that ARTHUR W. BURWI'JLL, a citizen of the United States,residing at Poughkeepsie, in the county of Dutchess and State of NewYork, have invented certain new and useful Improvements in Processes ofProducing Chromic-Acid Solutions, of which the following is aspecification.

Inan application filed concurrently herewith, Ser. No. 531,281, I havedescribed and claimed a process of oxidizing chromic salt solutions bycausing the same to flow successively through the cathode and anodecompartments of an electrolytic cell having a porous diaphragm,employing certain precautions having the effect of insuring a highdegree of efficiency in the utilization of the current and a continuednormal operation of the process. Thus, in said process I preferahly usean anode consisting of cast metal, which may be lead; or a lead-antimonyalloy containing a comparatively small proportion -say up to 7 percentof antimony; or a lead-antimon y alloy presenting an vactive face oflead. In said process also I use sufficient excess of chromic salt inthe flowing electrolyte to avoid substantial evolution of oxygen at theanode. A preferred form of apparatus for use in connection with theabove recess comprises a containing vessel of lead or lead-antimonyalloy serving as the anode; a porous cup or vessel functioning as adiaphragm; and a cathode, which may be of sheet lead, within the latter.

According to the present invention I am able toprepare directly fromchromic hydroxid, a solution of chromic acid substantially free fromsulfuric acid. The apparatus employed may be the same as that used forthe oxidation of chromic salt solutions;

as mentioned above; but in the present process it is unnecessary toprovide fora continuous flow of solutions.

In practicing the present invention I provide an electrolytic cellhaving a porous diaphragm of acid resisting material such as filtros,porous earthenware 'or the like.

Both

Application filed January 23, 1922. Serial No. 531,282.

electrodes may be of lead, or a lead-antimony alloy containing about35-70% of antimony as described above, cast metal being preferably usedin either case. The solution surrounding thecathode may consist ofdilute sulfuric acid, or alternatively of any soluble sulfate. The anodecompartment contains initiall a suspension or magma ol chromic hy roxidin water, slightly acidulated with sulfuric acid, or containing a smalladdition of a soluble sulf ate such as chromic sulfate, sodium sulfate,etc. Upon passage of the electric current the chromic hydroxid isprogressively, and eventually completely, oxidized to chromic acid.Preferably the proportion of chromic hydroxid to water in the originalcharge is such that the concentration of (110;, in the final solutionwill approximate but not excecd 1077. Anode current densities of theorder of 18 amperes per square foot are preferred, with cathode currentdensities of the order of 100-200 amperes; 8595 C. is a favorableworking temperature. The process is most conveniently operatedintermittently; but it is within my invention to provide for continuousor semi-continuous o-poration, the chromic acid solution being withdrawnfrom. the anode compartment, and the equivalent quantities of chromichydroxid and water supplied thereto.

I claim i 1. Process of producing chromic acid solutions which consistsin subjecting a magma or suspension comprising chromic hydroxid andwater to anodicoxidation.

2. Process according to claim 1 in which thedanodes present activesurfaces of cast lea v 3. Process according to claim 1 in which theanode consists of a cast alloy of lead and antimony, said alloycontaining a relatively small proportion of antimony.

In testimony whereof, I aflix my signature,

